WO2011122019A1

WO2011122019A1 - Fuel cell system and method for driving same

Info

Publication number: WO2011122019A1
Application number: PCT/JP2011/001902
Authority: WO
Inventors: 梅田　孝裕; 日下部　弘樹; 安本　栄一; 鵜木　重幸; 菅原　靖; 柴田　礎一; 酒井　修
Original assignee: パナソニック株式会社
Priority date: 2010-03-30
Filing date: 2011-03-30
Publication date: 2011-10-06
Also published as: JP5049413B2; EP2555298A4; EP2555298A1; JPWO2011122019A1; KR20130023223A; US20130017458A1

Abstract

A controller (15) conducts a termination operation in which the generation of an electric power by a fuel cell (3) is terminated, and subsequently conducts an activity recovery operation in which the supply of a fuel gas to be supplied to an anode (2a) by means of a fuel gas supply unit (10) is terminated, an inert gas is supplied to the anode (2a) by means of an anode inert gas supply unit (13), and an oxidizing agent gas is supplied to the cathode (2b) by means of an oxidizing gas supply unit (11). In this manner, the controller (15) can control so that the fuel gas supply unit (10) can re-start the supply of the fuel gas to the anode (2a) and the fuel cell (3) can re-start the generation of an electric power after the battery voltage of the fuel cell (3) which is detected by a voltage detector (14) is decreased to a first voltage or lower.

Description

Fuel cell system and operation method thereof

The present invention relates to a fuel cell system in which deterioration of the fuel cell due to impurities is suppressed and durability is improved, and an operation method thereof.

As shown in FIG. 10, the conventional general fuel cell system includes an anode 22a supplied with fuel gas and an anode 22b supplied with oxidant gas, which are provided facing each other with an electrolyte 21 therebetween. A stack formed by stacking a plurality of fuel cells 23 is provided.

The fuel gas and the oxidant gas are supplied to the anode 22a and the cathode 22b through the separators 24a and 24b provided with the respective gas flow paths.

A fuel gas supply unit that supplies fuel gas to the anode inlet and an oxidant gas supply unit that supplies oxidant gas to the cathode inlet are connected to the stack configured as described above, and a desired power generation state is achieved by the controller. So that it is controlled.

Fuel cell systems are required to have both long-term durability of about 10 years and cost reduction for their spread. On the other hand, conventionally, this type of fuel cell system is affected by various impurities, the battery voltage is lowered, the power generation efficiency is lowered, and the durability is sometimes lowered. As a method for improving durability when affected by impurities, it is conceivable to increase the amount of catalyst (for example, platinum-based catalyst) used for the anode and cathode of the fuel cell, but from the viewpoint of cost reduction Is not preferred.

The impurities include internal impurities generated from members such as resin parts and metal parts constituting the fuel cell system, and external impurities mixed from the outside such as the atmosphere, and these impurities are used for the anode 22a and the cathode 22b. There is a risk that the battery voltage of the fuel cell 23 is lowered by poisoning and reducing the activity of the catalyst.

In order to remove the influence of impurities such as CO that poison the platinum-based catalyst of the anode 22a in particular, the conventional fuel cell system has a constant current when, for example, the battery voltage of the fuel cell 23 becomes 0.6V or less. While the power generation of the fuel cell 23 is continued in the discharged state, the supply of the fuel gas supplied by the fuel gas supply unit is temporarily stopped, and the CO having adsorbed the electrode potential of the anode 22a to the anode 22a is electrochemically oxidized. And a technique for oxidizing and removing CO adsorbed on the anode 22a is disclosed (for example, refer to the second embodiment of Patent Document 1).

Japanese Patent No. 3536645

However, as in the conventional fuel cell system, in the method in which impurities accumulate in the anode and the cell voltage of the fuel cell decreases and then the anode electrode potential is increased, the impurities in the anode decrease as the cell voltage decreases. However, the fuel cell is gradually deteriorated and the durability is lowered.

For example, Patent Document 1 discloses a technique of removing impurities such as CO adsorbed on the surface of the fuel electrode during operation by temporarily stopping the supply of fuel to the electrode of the fuel cell. (See paragraph 0035). Specifically, it is described that the fuel supply is stopped when the battery voltage falls below 0.6V under a constant current discharge state, and the fuel supply is restarted when the battery voltage becomes 0.1V. (See, for example, paragraph 0026, paragraph 0030, paragraph 0032, FIGS. 3 and 4).

However, from the viewpoint of suppressing anode deterioration when the anode electrode potential is increased and impurities are removed by oxidation, there is still room for improvement in the impurity removal technique described in Patent Document 1. It is done.

SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide a fuel cell system excellent in durability by more reliably removing impurities adsorbed on an anode and suppressing deterioration of the fuel cell. .

As a result of intensive studies, the present inventors have found a problem that the deterioration of the fuel cell may progress although the voltage decrease is hardly observed because the impurity does not greatly contribute to the voltage decrease of the fuel cell. It was.

Specifically, when impurities accumulate in the anode of the fuel cell and react with oxygen that cross-leaks from the cathode to generate hydrogen peroxide on the anode side, a chemical reaction occurs, and a radical species with a very strong oxidizing power on the anode side. Produces. When an electrolyte membrane containing a resin or a catalyst layer is in contact with this radical species for a long time, the resin gradually decomposes and deteriorates. However, at this time, the battery voltage of the fuel cell does not necessarily decrease. In the conventional fuel cell system, when there is almost no voltage drop, the anode impurities cannot be sufficiently removed.

In particular, when the amount of platinum in the anode is reduced in order to reduce the cost of the fuel cell, the present inventors become more prominent, and there is still room for improvement from the viewpoint of durability of the fuel cell. I found.

In order to solve the above conventional problems, a fuel cell system according to the present invention includes a fuel cell having an anode and a cathode, a fuel gas supply unit, an oxidant gas supply unit, an anode inert gas supply unit, and a voltage detection. And a controller, and the controller performs a stop operation to stop power generation of the fuel cell, and then stops the supply of the fuel gas that the fuel gas supply unit supplies to the anode, and the anode An inert gas supply unit supplies the inert gas to the anode, and the oxidant gas supply unit supplies the oxidant gas to the cathode, and performs an activity recovery operation, which is detected by the voltage detector. After the battery voltage of the fuel cell drops below the first voltage, the fuel gas supply unit resumes supplying the fuel gas supplied to the anode, and resumes power generation of the fuel cell. It is intended to cormorants control.

Thus, when a predetermined time has elapsed (for example, every time a first period estimated to accumulate an amount of impurities that does not affect the deterioration of the fuel cell has elapsed), the electrode potential of the anode is increased. Thus, the anode impurities are removed, so that deterioration of the fuel cell can be suppressed.

In addition, since the anode flow path is replaced with an inert gas after the fuel gas supply is stopped, the fuel (hydrogen) concentration in the anode is reduced, and the time until the anode electrode potential is sufficiently increased is shortened. Can do. Therefore, the time for which the electrode potential of the anode is sufficiently increased can be shortened, and impurities in the anode can be sufficiently removed while suppressing deterioration of the anode. In addition, if it takes too much time for the anode electrode potential to rise sufficiently, impurities in the anode can be removed. For example, oxidation of carbon holding the catalyst of the anode, oxidation degradation of the resin, elution due to oxidation of Ru, etc. May occur and the anode may deteriorate.

According to the fuel cell system of the present invention, before the impurities affect the deterioration of the fuel cell, it is possible to stop the power generation of the fuel cell and raise the electrode potential of the anode to remove the impurities of the anode, It is possible to obtain a fuel cell system with excellent durability in which deterioration of the fuel cell due to impurities is suppressed.

1 is a schematic configuration diagram of a fuel cell system according to Embodiment 1 of the present invention. Flow chart showing the operation sequence of the system The flowchart which shows the operation sequence of the fuel cell system in Embodiment 2 of this invention. The flowchart which shows the operation sequence of the fuel cell system in Embodiment 3 of this invention. Characteristic chart showing power generation characteristics and changes in fluorine ion concentration The flowchart which shows the operation sequence of the fuel cell system in Embodiment 4 of this invention. The flowchart which shows the operation sequence of the fuel cell system in Embodiment 5 of this invention. The flowchart which shows the operation sequence of the fuel cell system in Embodiment 6 of this invention. Schematic configuration diagram of a fuel cell system according to Embodiment 9 of the present invention Schematic configuration diagram of a conventional fuel cell system

A first invention includes a fuel cell having an anode and a cathode, a fuel gas supply unit for supplying a fuel gas containing at least hydrogen to the anode, and an oxidant gas supply for supplying an oxidant gas containing at least oxygen to the cathode. An anode inert gas supply unit that supplies an inert gas to the anode and replaces at least a part of the fuel gas with the inert gas, and a voltage detector that detects a battery voltage of the fuel cell. A controller for controlling operations of the fuel cell, the fuel gas supply unit, the oxidant gas supply unit, and the anode inert gas supply unit, and the controller stops the power generation of the fuel cell. Then, the fuel gas supply unit stops supplying the fuel gas to the anode, and the anode inert gas supply unit supplies the inert gas to the front. The battery voltage of the fuel cell, which is supplied to the anode and the oxidant gas supply unit supplies the oxidant gas to the cathode and performs an activity recovery operation and is detected by the voltage detector, is a first voltage. The fuel gas supply unit performs control so as to resume supply of the fuel gas supplied to the anode and resume power generation of the fuel cell after being lowered to the following.

With this configuration, the anode electrode potential is not increased after the cell voltage of the fuel cell has decreased, but an amount of impurities that does not affect the deterioration of the fuel cell accumulates after a predetermined time has elapsed. (Every time the estimated first period elapses ) , the electrode potential of the anode is increased, so that the impurities do not contribute to the voltage drop of the fuel cell, but even if it contributes to the deterioration of the fuel cell, the anode and cathode The impurities can be removed and deterioration of the fuel cell can be suppressed.

Also, instead of increasing the electrode potential of the anode by supplying air directly to the anode, the anode inert gas supply unit replaces the fuel gas containing hydrogen remaining in the anode with an inert gas, and supplies the oxidant gas. The unit supplies air to the cathode and cross-leaks oxygen in the air through the electrolyte membrane to indirectly increase the electrode potential of the anode, so there is no need to add a configuration for supplying air to the anode. The battery system can be simplified and the cost can be reduced.

In addition, when the anode fuel gas is replaced with an inert gas and oxygen is supplied from the cathode to the anode through the electrolyte membrane, the anode electrode potential rises and the apparent cell voltage (potential difference with the cathode) is It becomes 1st voltage (for example, about 0.1V) or less. This battery voltage is detected by a voltage detector, and when the first voltage is reached, the supply of fuel gas and oxidant gas is started and the power generation of the fuel cell is resumed, so that more oxygen than necessary is not supplied to the anode. The oxidation of the anode catalyst can be minimized.

In addition, every time a first period in which it is estimated that an amount of impurities that does not affect the deterioration of the fuel cell accumulates, the power generation of the fuel cell is stopped, and the electrode potential of not only the anode but also the cathode As a result, the impurities remaining inside the fuel cell poisoned to the anode and the cathode, or impurities generated by thermal decomposition of the members constituting the fuel cell during the operation of the fuel cell are oxidized and removed. Thus, a fuel cell system excellent in power generation efficiency and durability in which voltage drop due to impurities is suppressed can be obtained.

In a second aspect based on the first aspect, the controller stops power generation of the fuel cell, stops supply of the oxidant gas supplied to the cathode by the oxidant gas supply unit, and supplies the fuel. A gas supply unit stops the supply of the fuel gas supplied to the anode, and performs a stop operation.
Control is performed so that the activation recovery operation is performed after the battery voltage of the fuel cell detected by the voltage detector drops below a second voltage.

With this configuration, after stopping the power generation of the fuel cell, before raising the electrode potential of the anode and the cathode, the supply of the oxidant gas and the fuel gas to the cathode and the anode is temporarily stopped, By reacting and consuming oxygen remaining on the cathode with hydrogen that cross leaks from the anode, the catalyst at the cathode electrode interface is reduced, and the activity of the catalyst can be recovered.

At this time, since the oxygen at the catalyst interface of the cathode disappears, the electrode potential of the cathode decreases, and the apparent battery voltage (potential difference between the anode and cathode) detected by the voltage detector decreases and is detected by the voltage detector. After the battery voltage reaches the second voltage or less at which the activity of the catalyst of the cathode sufficiently recovers, a certain amount of inert gas is supplied to the anode by the anode inert gas supply unit, and again by the oxidant gas supply unit. A certain amount of oxidant gas is supplied to the cathode to raise the electrode potential of the anode and the cathode, keep the catalytic activity of the anode and the cathode high and oxidize and remove impurities, so that a high battery voltage is maintained for a long time. Thus, a fuel cell system excellent in power generation efficiency and durability can be obtained.

According to a third invention, in the first invention or the second invention, a cooling unit for cooling the fuel cell and a temperature detector for detecting the temperature of the fuel cell are provided, and the controller is configured to control the fuel. The power generation of the battery is stopped, and the stop operation for controlling the cooling unit to cool the fuel cell is performed, and the temperature of the fuel cell detected by the temperature detector is reduced to a first temperature or lower. Thereafter, control is performed to perform the activity recovery operation.

With this configuration, the fuel cell is cooled to a low temperature (below the first temperature), so that moisture in the electrode is likely to condense. When moisture in the electrode is condensed, impurities attached to the electrode are dissolved in the condensed water, so that it is easy to remove.

In addition, when power generation of the fuel cell is stopped, the water vapor contained in the fuel gas and oxidant gas supplied during power generation and the water vapor generated by the reaction are cooled and condensed, and condensed water is generated at each of the anode and the cathode. Is done. Among the impurities remaining inside when creating the fuel cell, or impurities generated by thermal decomposition of the members constituting the fuel cell during the operation of the fuel cell, water-soluble impurities dissolve in this condensed water, Stopped condensed water that has absorbed the impurities can be discharged out of the system together with the inert gas or oxidant gas supplied in the next step.

In this case, the timing of power generation stop and cooling may not be the same. For example, power generation may be stopped, cooling may be performed after a second period (described later), cooling may be performed, and power generation may be stopped after the second period.

According to a fourth invention, in the third invention, a cooling unit for cooling the fuel cell, and a temperature detector for detecting the temperature of the fuel cell, wherein the controller is detected by the temperature detector. Controlling the cooling unit so that the temperature of the fuel cell is equal to or lower than the first temperature, and stopping the power generation of the fuel cell after performing the power generation of the fuel cell for a second period. Control is performed so as to perform the activity recovery operation after that.

This configuration generates power at a low temperature (below the first temperature), so that moisture generated by power generation is more easily condensed at the electrode. Therefore, the amount of water condensed at the electrode is increased, and impurities attached to the electrode are easily dissolved.

In addition, before the power generation is stopped, the temperature of the fuel cell is controlled to be equal to or lower than a predetermined temperature, the anode and the cathode are excessively humidified, and a large amount of condensed water is generated at the anode and the cathode. By continuing the power generation for a period, the contamination of the anode and the cathode is absorbed by the condensed water and discharged together with the fuel gas and the oxidant gas, respectively, and the amount of contamination can be further reduced until the power generation stops.

According to a fifth invention, in any one of the first to fourth inventions, a cooling unit for cooling the fuel cell and a temperature detector for detecting a temperature of the fuel cell are provided, and the controller includes the fuel In the start-up operation of the battery, the cooling unit is controlled so that the temperature of the fuel cell is equal to or lower than the second temperature, and the power generation of the fuel cell is controlled to be performed for a third period. .

This configuration generates power at a low temperature (below the second temperature), so that water generated by power generation is more easily condensed at the electrode. Therefore, the amount of water condensed at the electrode is increased, and impurities attached to the electrode are easily dissolved.

In addition, power is generated when the temperature of the fuel cell is low at start-up, the anode and cathode become over-humidified, a large amount of condensed water is generated at the anode and cathode, and contamination of the anode and cathode is absorbed by the condensed water. It is discharged out of the system together with the fuel gas and oxidant gas, and the amount of contamination can be reduced.

In a sixth aspect based on any one of the first to fifth aspects, the controller stops the supply of the fuel gas supplied to the anode by the fuel gas supply unit, and the anode inert gas supply unit After supplying the inert gas to the anode, the oxidant gas supply unit is controlled to perform an activity recovery operation of supplying the oxidant gas to the cathode.

With this configuration, the anode inert gas supply unit replaces the fuel gas containing hydrogen remaining in the anode with the inert gas, expels the hydrogen that reacts with oxygen, stops the supply of the inert gas, and After that, the oxidant gas supply unit supplies the oxidant gas to the cathode, so that the amount of oxygen that cross-leaks through the electrolyte membrane can be increased, and the electrode potential of the anode can be increased in a shorter time. Since the period during which the anode catalyst is exposed to a high potential can be shortened, the oxidation of the anode catalyst can be further suppressed.

In a seventh aspect based on any one of the first to sixth aspects, the controller performs the stop operation every time the first period elapses, and then performs the activity recovery operation. Control is made so that the power generation of the fuel cell is resumed.

In an eighth aspect based on the seventh aspect, the first period controlled by the controller is a time when the power generation time integrated value obtained by integrating the power generation times of the fuel cells has reached a predetermined power generation integration time. It is characterized by.

With this configuration, the integrated value of the power generation time, such as impurities generated by thermal decomposition of the members constituting the fuel cell during operation of the fuel cell, impurities contained in the fuel gas or oxidant gas supplied from the outside, etc. First, it is estimated that an amount of impurities that do not affect the deterioration of the fuel cell is accumulated by experimentally calculating in advance the power generation time at which the impurities related to the fuel cell start to affect the deterioration of the fuel cell. Each time the period elapses, the power generation of the fuel cell is stopped, the electrode potentials of the anode and the cathode are raised, and the impurities of the anode and the cathode are oxidized and removed, so that deterioration of the fuel cell can be suppressed.

According to a ninth invention, in any one of the first to eighth inventions, the anode inert gas supply unit includes a desulfurizer for desulfurizing a raw material gas, and the inert gas is a raw material gas desulfurized by the desulfurizer. It is characterized by being.

With this configuration, since the raw material gas having a low activity with respect to the fuel cell is used as the inert gas in the operating environment of the fuel cell, the configuration of the fuel cell system is compared with the case where a gas cylinder such as nitrogen is used as the inert gas. Thus, the cost can be reduced and the installation of the fuel cell system can be improved.

According to a tenth aspect of the present invention, in any one of the first to ninth aspects, the anode inert gas supply unit is configured to supply the inert gas to the anode via the fuel gas supply unit. Features.

With this configuration, it is not necessary to add a configuration for supplying the inert gas directly to the anode of the fuel cell. Therefore, the fuel cell system can be simplified, the cost can be reduced, and the fuel gas supply unit can be purged with the inert gas. Therefore, deterioration due to oxidation of the catalyst used in the fuel gas supply unit can be suppressed, and the durability of the fuel cell system can be further improved.

An eleventh aspect of the invention is an operation of a fuel cell system including a fuel cell having an anode and a cathode, supplying a fuel gas containing at least hydrogen to the anode, and supplying an oxidant gas containing at least oxygen to the cathode to generate electric power. A method of stopping the power generation of the fuel cell; and thereafter, stopping the supply of the fuel gas to the anode, supplying the inert gas to the anode, and oxidizing including at least oxygen Supplying an agent gas to the cathode, and after the battery voltage of the fuel cell has dropped below a first voltage, the supply of the fuel gas to the anode is resumed, and the fuel cell A restarting step for restarting power generation.

As described above, the anode electrode potential is not increased after the battery voltage of the fuel cell is lowered, but when a predetermined amount of time has elapsed (for example, an amount of impurities that does not affect the deterioration of the fuel cell is accumulated). Every time the estimated first period elapses), the electrode potential of the anode is raised so that impurities do not contribute to the voltage drop of the fuel cell, but even if it contributes to the degradation of the fuel cell, the anode and cathode Impurities can be removed and deterioration of the fuel cell can be suppressed.

In a twelfth aspect based on the eleventh aspect, the stopping step stops power generation of the fuel cell, stops supply of the oxidant gas supplied to the cathode, and supplies the fuel gas supplied to the anode. A step of stopping supply, and after the stop step, the activity recovery step is performed after the cell voltage of the fuel cell has dropped to a second voltage or less.

As described above, after stopping the power generation of the fuel cell and before increasing the electrode potential of the anode and the cathode, the supply of the oxidant gas and the fuel gas to the cathode and the anode is temporarily stopped, and the cathode The oxygen remaining in the catalyst reacts with hydrogen that cross leaks from the anode and is consumed, whereby the catalyst at the cathode electrode interface is reduced and the activity of the catalyst can be recovered.

In a thirteenth aspect based on the eleventh or twelfth aspect, the stopping step is a step of stopping power generation of the fuel cell and cooling the fuel cell, wherein the temperature of the fuel cell is the first level. The activity recovery step is performed after the temperature falls below the temperature of the above.

In this case, the timing of power generation stop and cooling may not be the same. For example, power generation may be stopped, cooling may be performed after the second period, cooling may be performed, and power generation may be stopped after the second period.

In a fourteenth aspect based on the thirteenth aspect, the fuel cell is cooled so that the temperature of the fuel cell is equal to or lower than the first temperature, and the power generation of the fuel cell is performed for the second period. The power generation of the fuel cell is stopped, the stop step is performed, and then the activity recovery step is performed.

As described above, since power is generated at a low temperature (below the first temperature), moisture generated by the power generation is more easily condensed at the electrode. Therefore, the amount of water condensed at the electrode is increased, and impurities attached to the electrode are easily dissolved.

In a fifteenth aspect of the invention according to any one of the eleventh to fourteenth aspects, the fuel cell is cooled such that the temperature of the fuel cell is equal to or lower than the second temperature during the start-up operation of the fuel cell. The power generation of the fuel cell is performed for a third period.

As described above, since power is generated at a low temperature (below the second temperature), water generated by the power generation is more easily condensed at the electrode. Therefore, the amount of water condensed at the electrode is increased, and impurities attached to the electrode are easily dissolved.

In a sixteenth aspect based on any one of the eleventh to fifteenth aspects, the activity recovery step stops the supply of the fuel gas supplied to the anode by the fuel gas supply unit, and the anode inert gas supply unit After supplying the inert gas to the anode, the oxidant gas supply unit supplies the oxidant gas to the cathode.

As described above, the anode inert gas supply unit replaces the fuel gas containing hydrogen remaining in the anode with the inert gas, expels hydrogen that reacts with oxygen, stops the supply of the inert gas, After reducing the internal pressure, the oxidant gas supply section supplies the oxidant gas to the cathode, so the amount of oxygen that cross-leaks through the electrolyte membrane can be increased, and the electrode potential of the anode is increased in a shorter time. In addition, since the period during which the anode catalyst is exposed to a high potential can be shortened, oxidation of the anode catalyst can be further suppressed.

In a seventeenth aspect based on any one of the eleventh to sixteenth aspects, the stop step is performed every time the first period elapses, and then the reactivation step is performed after performing the activity recovery step. It is characterized by.

In an eighteenth aspect based on the seventeenth aspect, the first period is a time when a power generation time integrated value obtained by integrating the power generation times of the fuel cells reaches a predetermined power generation integration time.

As described above, the accumulated value of the power generation time such as impurities generated by thermal decomposition of the members constituting the fuel cell during operation of the fuel cell, impurities contained in the fuel gas or oxidant gas supplied from the outside, etc. It is estimated that the amount of impurities that do not affect the deterioration of the fuel cell is accumulated by experimentally obtaining in advance the power generation time at which the relevant impurity starts to affect the deterioration of the fuel cell. Each time the period elapses, the power generation of the fuel cell is stopped, the electrode potentials of the anode and the cathode are raised, and the impurities of the anode and the cathode are oxidized and removed, so that deterioration of the fuel cell can be suppressed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same reference numerals are given to the same components as those of the above-described embodiments, and detailed description thereof will be omitted. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a schematic configuration diagram showing a fuel cell system according to Embodiment 1 of the present invention.

As shown in FIG. 1, the fuel cell system according to Embodiment 1 of the present invention includes a fuel cell 3 in which an anode 2a and a cathode 2b are formed opposite to each other on an electrolyte 1 side.

Here, the electrolyte 1 is composed of, for example, a solid polymer electrolyte made of a perfluorocarbon sulfonic acid polymer having hydrogen ion conductivity.

The anode 2a and the cathode 2b are formed on a catalyst layer made of a mixture of a catalyst in which a noble metal such as platinum is supported on porous carbon having high oxidation resistance and a polymer electrolyte having hydrogen ion conductivity. It is composed of a laminated gas diffusion layer having air permeability and electronic conductivity.

At this time, a platinum-ruthenium alloy catalyst that suppresses poisoning by impurities contained in the fuel gas, particularly carbon monoxide, is generally used as the catalyst for the anode 2a.

Also, as the gas diffusion layer, carbon paper or carbon cloth subjected to water repellent treatment, carbon non-woven fabric, or the like is used.

The anode separator 4a and the cathode separator 4b are arranged so as to face each other with the fuel cell 3 interposed therebetween, and the fuel gas flow for supplying and discharging the fuel gas to the surface of the anode separator 4a on the fuel cell 3 side An oxidant gas passage 41b for supplying and discharging an oxidant gas is formed on the surface of the cathode side separator 4b on the fuel cell 3 side of the passage 41a.

Further, a cooling fluid passage 5 for supplying and discharging a cooling fluid for cooling the fuel cell 3 is formed on the surface of the cathode side separator 4b opposite to the fuel cell 3 side. The cooling fluid channel 5 may be formed on the surface of the anode separator 4a opposite to the fuel cell 3 side, or an independent cooling plate on which the cooling fluid channel 5 is formed may be provided separately.

Here, the anode side separator 4a and the cathode side separator 4b are mainly formed of a conductive material such as carbon.

The anode-side separator 4a and cathode-side separator 4b and the fuel cell 3 are sealed by an anode-side gasket 6a and a cathode-side gasket 6b, respectively, so that the respective fluids do not leak to different fluid flow paths and the outside.

Then, a plurality of cells composed of the fuel cell 3 and the

separators

4a and 4b configured as described above are stacked, a current collector 7 is disposed at both ends to extract current, an end plate 8 is disposed via an insulator, The stack was formed by fastening. A heat insulating material 9 was disposed around the stack in order to prevent heat dissipation to the outside and increase the exhaust heat recovery efficiency.

Then, a fuel gas supply unit 10 for supplying a fuel gas containing hydrogen to the anode 2a side, an oxidant gas supply unit 11 for supplying an oxidant gas containing oxygen in the atmosphere to the cathode 2b side, and the stack are cooled, A cooling unit 12 that supplies a cooling fluid that exchanges heat with heat generated in the stack was connected.

Here, the fuel gas supply unit 10 desulfurizes the sulfur compound, which is a catalyst poisoning substance, from a raw material gas such as city gas (a hydrocarbon gas mainly containing methane, which is supplied using piping in a city). The apparatus 101 includes a raw material gas supply unit 102 that controls the flow rate of the desulfurized raw material gas, and a hydrogen generation unit 103 that reforms the desulfurized raw material gas to generate hydrogen. Moreover, the desulfurizer 101 and the raw material gas supply part 102 are called the anode inert gas supply part 13 as needed.

Furthermore, the hydrogen generation unit 103 includes at least a reforming unit, a carbon monoxide conversion unit, and a carbon monoxide removal unit.

At the time of stoppage, the anode inert gas supply unit 13 can supply the anode 2a with a raw material gas that is less active with respect to the anode 2a, and can replace at least a part of the fuel gas remaining in the anode 2a. Configured. A bypass channel 131 that bypasses the hydrogen generator 103 is connected, and the hydrogen generator 103 and the bypass channel 131 are switched using a valve.

Here, the configuration is such that the inert gas is supplied to the anode 2a via the bypass channel 131, but the present invention is not limited to this, and the reforming of the raw material gas is performed while the hydrogen generator 103 is stopped or at a low temperature. When the reaction does not occur, an inert gas (raw material gas) may be supplied to the anode 2a through the hydrogen generator 103 (for example, see Embodiment 7 described later).

Next, the operation performed by the fuel gas supply unit 10 will be briefly described. For example, when methane is used as the raw material gas, the reaction shown in (Chemical Formula 1) and (Chemical Formula 2) occurs in the reforming unit with water vapor, and hydrogen is generated.

In addition, the reaction shown in (Chemical Formula 3) is performed by summing up all reactions occurring in the reforming section.

However, the reformed gas produced in the reforming section contains about 10% carbon monoxide in addition to hydrogen. And carbon monoxide poisons the catalyst contained in the anode 2a in the operating temperature range of the fuel cell 3, and lowers its catalytic activity. Therefore, carbon monoxide generated in the reforming section is converted into carbon dioxide in the carbon monoxide conversion section as shown in the reaction formula (Chemical Formula 2). This reduces the concentration of carbon monoxide to about 5000 ppm.

Furthermore, carbon monoxide with a reduced concentration is selectively oxidized with oxygen taken from the atmosphere or the like by the reaction indicated by (Chemical Formula 4) in the carbon monoxide removal section. As a result, the concentration of carbon monoxide is reduced to about 10 ppm or less which can suppress a decrease in the catalytic activity of the catalyst of the anode 2a.

In addition, by providing air bleed means for supplying air to the anode 2a during power generation and mixing about 1 to 2% of air with the hydrogen gas generated by the fuel processor 103, the effect of the slight remaining carbon monoxide. Can be further reduced.

The fuel gas supply unit 10 is not limited to the steam reforming method, but may be a hydrogen generation method such as an autothermal method. If the concentration of carbon monoxide contained in the fuel gas is low, the air bleed means is omitted. be able to.

The oxidant gas supply unit 11 includes an oxidant gas flow rate controller 111 that controls the flow rate of the oxidant gas, impurity removal means 112 that removes impurities in the oxidant gas to some extent, and humidification that humidifies the oxidant gas. Consists of means 113.

Here, the oxidant gas is a general term for gases containing at least oxygen (or capable of supplying oxygen). For example, the atmosphere (air) is used.

Furthermore, the impurity removing means 112 includes a dust removing filter that removes dust in the atmosphere, a sulfur-based impurity such as sulfur dioxide and hydrogen sulfide, and an acid gas removing filter that removes acid gases in the atmosphere such as nitrogen oxides, It consists of an alkaline gas removal filter that removes alkaline gas such as ammonia in the atmosphere. Each filter can be omitted depending on the installation environment and the contamination resistance of the fuel cell 3.

The cooling unit 12 passes through the cooling fluid tank 121 that stores the cooling fluid that cools the stack, the cooling fluid pump 122 that supplies the cooling fluid, and the cooling fluid channel 5, and generates heat and heat generated in the fuel cell 3. The heat exchanger 123 is configured to make hot water by further exchanging heat with the exchanged cooling fluid.

And a voltage detector 14 was connected to the stack in order to detect the battery voltage of the stack.

In addition, the controller 15 controls the start, power generation, and stop operations of the fuel cell 3, and the fuel gas supply unit 10, the oxidant gas supply unit 11, the anode inert gas supply unit 13, the cooling unit 12, and the like. Can be controlled.

Next, the operation of the fuel cell system configured as described above during power generation will be described with reference to FIG.

First, in FIG. 1, when the fuel gas is supplied to the anode 2a and the oxidant gas is supplied to the cathode 2b, and the controller 15 is controlled to connect the load to the fuel cell 3, the hydrogen in the fuel gas is expressed by the reaction formula (Formula 5). ), Electrons are released at the interface between the catalyst layer of the anode 2a and the electrolyte 1 to form hydrogen ions.

The released hydrogen ions move to the cathode 2b through the electrolyte 1 and receive electrons at the interface between the catalyst layer of the cathode 2b and the electrolyte 1. At this time, it reacts with oxygen in the oxidant gas supplied to the cathode 2b to generate water as shown in the reaction formula (Formula 6).

When the above reactions are combined, the reaction shown in (Chemical Formula 7) is performed.

The flow of electrons flowing through the load can be used as direct current electric energy. Further, since the series of reactions described above is an exothermic reaction, the heat generated in the fuel cell 3 is recovered by exchanging heat with the cooling fluid supplied from the cooling fluid flow path 5 to recover the heat energy such as hot water. can do.

By the way, the oxidant gas used for power generation of the fuel cell 3 is usually the atmosphere in the environment in which it is installed, but the atmosphere often contains various impurities, such as volcanoes and combustion. There are sulfur compounds such as sulfur dioxide contained in exhaust gas, nitrogen oxides abundantly contained in combustion exhaust gas of factories and automobiles, and ammonia which is a malodorous component.

Further, the anode 2a and the cathode 2b of the fuel cell 3 are subjected to thermal decomposition of impurities remaining inside when the fuel cell is formed, and members (for example, an electrolyte) constituting the fuel cell during the operation of the fuel cell 3. Impurities generated or impurities generated from piping or parts used in the fuel cell system may be mixed.

These impurities adversely affect the fuel cell 3 and may be adsorbed on the catalyst of the anode 2a or the cathode 2b to hinder a chemical reaction necessary for power generation, thereby reducing the output of the fuel cell 3. When the impurities are accumulated, the polarization of the anode 2a is not so large from the beginning, and thus hardly appears in the voltage drop of the fuel cell 3.

On the other hand, if impurities exist in the anode 2a of the fuel cell 3, it reacts with oxygen that cross leaks from the cathode 2b and reacts with hydrogen peroxide generated on the anode 2a side, causing a chemical reaction, and oxidizing power is generated on the anode 2a side. Extremely strong radical species are generated. When the electrolyte layer 1 containing the resin and the catalyst layer of the anode 2a or the cathode 2b come into contact with this radical species for a long time, the resin gradually decomposes and the fuel cell 3 deteriorates. When the battery voltage starts to drop, the fuel cell 3 may be deteriorated so that it cannot be recovered.

By the way, the impurities adsorbed on the anode 2a and the cathode 2b are oxidized when the electrode potential of the anode 2a and the cathode 2b rises to the oxidation-reduction potential at which the respective impurities are oxidized, and the adsorbing power with the anode 2a or the cathode 2b becomes weak. It becomes easy to desorb from the anode 2a or the cathode 2b by being gasified or ionized.

The electrode potential at which each impurity is oxidized is determined by the type of impurity, the type of electrode, temperature, pH, and the like, but the inventors of the present invention particularly consider the anode 2a that is held in a state where the electrode potential is low during normal power generation. As a result of diligent investigation focusing on the impurities that poison the substrate, it was found that the impurities adsorbed on the anode 2a can be removed by oxidation by increasing the electrode potential of the anode 2a. For example, it has been found that by raising the electrode potential of the anode 2a to 0.5 to 1.2 V, impurities such as organic substances having an oxidation peak around 1.0 V can be oxidized and removed.

In addition, a time for accumulating an amount of impurities that does not affect the deterioration of the fuel cell 3 is experimentally obtained in advance, and the power generation of the fuel cell 3 is stopped every time this first period elapses. Then, it was found that deterioration of the fuel cell 3 can be suppressed by raising the electrode potential of the anode 2a and the cathode 2b during the stop and oxidizing and removing impurities poisoned to the anode 2a and the cathode 2b.

First, in order to determine a set value for the first period during which the controller 15 removes impurities, a power generation test of the fuel cell 3 having the same members and configuration as the fuel cell 3 used in the fuel cell system is performed, and the fuel in operation In order to quantify the deterioration of the battery 3, the concentration of fluorine ions contained in the drain water discharged from the anode 2a and the cathode 2b during power generation was analyzed.

Although only a very small amount of fluorine ions was detected for a while after the start of power generation, it was found that the elution amount of fluorine ions increased little by little after about 5,000 hours from the start of operation. This is because impurities remaining inside the fuel cell 3 during operation, impurities generated by thermal decomposition of members constituting the fuel cell 3, or pipes and parts used in the fuel cell system, etc. Impurities generated from the catalyst accumulate little by little, react with oxygen leaking from the cathode 2b and react with hydrogen peroxide produced on the anode 2a side, causing a chemical reaction, and on the anode 2a side, radicals with extremely strong oxidizing power It is presumed that the seeds are generated, and the resin 1 starts to decompose gradually as the electrolyte 1 containing the resin and the catalyst layer of the anode 2a or the cathode 2b come into contact with the radical species for a long time.

Note that at this time, the cell voltage of the fuel cell 3 was almost the same as the initial value, and it was found that it was difficult to detect the cell voltage initially even if the fuel cell 3 deteriorated.

The time during which the fuel cell 3 deteriorates due to this impurity greatly depends on the materials used for the electrolyte 1, the anode 2 a, and the cathode 2 b, the composition, the amount used, or operating conditions such as humidification and the operating temperature of the fuel cell 3. It is preferable to obtain for each configuration of the fuel cell 3 to be actually used, operating conditions, and the fuel cell system.

On the other hand, since the catalyst constituting the anode 2a is oxidized and deteriorated by increasing the electrode potential of the anode 2a, it is preferable that the time and number of times to increase the electrode potential of the anode 2a be as small as possible.

In view of the above, during the first period during which impurities accumulated in the fuel cell 3 are removed, the power generation time integrated value obtained by integrating the power generation time of the fuel cell 3 is about 1 in the fuel cell system according to Embodiment 1 of the present invention. In this first period, a sequence that suppresses the deterioration of the fuel cell 3 due to impurities is operated once. The first period may be a regular time that does not depend on the power generation time.

Further, the sequence for suppressing the deterioration of the fuel cell 3 due to impurities once in the first period needs to temporarily stop the power generation, but does not necessarily stop the power generation. If there is a timing when the fuel cell system stops before and after the time integrated value reaches a predetermined time, a sequence for suppressing deterioration of the fuel cell 3 due to impurities may be operated in accordance with the timing.

Hereinafter, an operation sequence of the fuel cell system capable of suppressing deterioration of the fuel cell due to impurities will be described with reference to the flowchart of FIG.

In FIG. 2, the controller 15 stops the power generation of the fuel cell 3 (step 102) when a predetermined time elapses (for example, reaches the first period) (step 101). Then, the fuel gas supplied to the anode 2a is stopped by the fuel gas supply unit 10, and the inert gas (desulfurized source gas) is supplied to the anode 2a by the anode inert gas supply unit 13 (step 103). At this time, a certain amount of inert gas necessary to replace the fuel gas remaining in the anode 2a with an inert gas is supplied to the anode 2a, and oxygen is cross-leaked into the anode 2a to cause the anode 2a to cross-leak. A certain amount of oxidant gas necessary to raise the electrode potential of 2a is supplied (step 104). In addition, it is preferable to increase / decrease the supply flow rate of oxidizing gas with respect to the supply flow rate during electric power generation as needed.

Further, the supply amount of the inert gas at this time is an amount necessary to replace the fuel gas remaining in the anode 2a, the supply amount of the oxidant gas is cross leaked oxygen, and the electrode potential of the anode 2a is the impurity potential. It is an amount necessary to increase the electrode potential to be oxidized, and it is preferable to obtain it experimentally in advance.

Note that, here, a certain amount of inert gas is supplied to the anode 2a and a certain amount of oxidant gas is supplied to the cathode 2b. However, the present invention is not limited to this. For example, the amount of inert gas supplied to the anode 2a may be different from the amount of oxidant gas supplied to the cathode 2b. Further, for example, an inert gas may be supplied to the anode 2a for a certain time, and an oxidant gas may be supplied to the cathode 2b for a certain time.

When a certain amount of inert gas and oxidant gas are supplied, the supply of the inert gas supplied by the anode inert gas supply unit 13 and the oxidant gas supplied by the oxidant gas supply unit 11 is stopped ( Step 105).

At this time, the electrode potential of the cathode 2b is about 1V, and the electrode potential of the anode 2a gradually rises from about 0V before the introduction of the inert gas by oxygen leaking from the cathode 2b, and approaches the electrode potential of the cathode 2b. Come. When the battery voltage detected by the voltage detector 14 (potential difference between the electrode potential of the anode 2a and the electrode potential of the cathode 2b) becomes equal to or lower than the first voltage (about 0.1 V), the electrode potential of the anode 2a is about It is determined that it is 0.9 V or more, and that part or all of the impurities such as organic substances having an oxidation peak around 1.0 V adsorbed on the anode 2a can be oxidized (step 106), and the fuel gas supply unit 10 again. The oxidant gas supply unit 11 is operated to supply the fuel gas and the oxidant gas to the anode 2a and the cathode 2b, respectively (step 107), and the power generation of the fuel cell 3 is resumed (step 108).

Here, step 104 and step 105 may be omitted and the process may proceed to step 106 after step 103. In this case, in Step 107, the supply of the inert gas to the anode 2a is stopped, the supply of the fuel gas to the anode 2a is started, and the supply of the oxidant gas to the cathode 2b may be continued.

The first voltage is related to the electrode potential necessary to oxidize the impurities adsorbed on the anode 2a, and is preferably experimentally determined in advance according to the impurities to be removed.

According to the fuel cell system of the first embodiment of the present invention configured as described above, the electrode potential of the anode 2a is not increased after the cell voltage of the fuel cell 3 is lowered, but the deterioration of the fuel cell 3 is affected. Since the electrode potential of the anode 2a is increased every time the first period estimated to accumulate a small amount of impurities, the impurities do not contribute to the voltage drop of the fuel cell 3. Even when contributing to the degradation, the impurities of the anode 2a and the cathode 2b can be removed, and the degradation of the fuel cell 3 can be suppressed.

Also, instead of increasing the electrode potential of the anode 2a by supplying air directly to the anode 2a, the anode inert gas supply unit 13 replaces the fuel gas containing hydrogen remaining in the anode 2a with an inert gas, The oxidant gas supply unit 11 supplies air to the cathode 2b, crosses the oxygen in the air through the membrane of the electrolyte 1, and indirectly increases the electrode potential of the anode 2a, so that air is supplied to the anode 2a. Therefore, it is not necessary to add a configuration to be realized, and the fuel cell system can be simplified and the cost can be reduced.

Further, when the fuel gas of the anode 2a is replaced with an inert gas and oxygen leaking from the cathode 2b is supplied to the anode 2a, the electrode potential of the anode 2a rises, and the apparent battery voltage (with respect to the cathode 2b) (Potential difference) is about 0.1 V or less. The battery voltage is detected by the voltage detector 14, and when the voltage becomes about 0.1 V or less, the supply of the fuel gas and the oxidant gas is started and the power generation of the fuel cell 3 is restarted. The oxidation of the catalyst of the anode 2a can be minimized.

Further, every time a first period in which the amount of impurities is estimated to accumulate so that the impurities do not affect the deterioration of the fuel cell 3, the power generation of the fuel cell 3 is stopped, and not only the anode 2a but also the cathode Since the electrode potential of 2b is also increased, impurities remaining inside the fuel cell 3 poisoned to the anode 2a and the cathode 2b or members constituting the fuel cell 3 during the operation of the fuel cell 3 are thermally decomposed. Thus, it is possible to oxidize and remove impurities generated, and to obtain a fuel cell system excellent in power generation efficiency and durability in which a voltage drop due to the impurities is suppressed.

(Embodiment 2)
In the fuel cell system according to Embodiment 2 of the present invention, the controller 15 stops the power generation of the fuel cell 3 every time the first period elapses, and the oxidant gas supply unit 11 supplies the cathode 2b with the oxidation. After the supply of the agent gas is stopped, the supply of the fuel gas supplied to the anode 2a is stopped by the fuel gas supply unit 10, and the battery voltage of the fuel cell 3 detected by the voltage detector 14 is lowered to the second voltage or lower. The anode inert gas supply unit 13 supplies an inert gas to the anode 2a, and the oxidant gas supply unit 11 supplies a certain amount of oxidant gas to the cathode 2b. .

The constituent elements other than the sequence in which the supply of the fuel gas and the oxidant gas is stopped after the power generation is stopped and the battery voltage is lowered to the second voltage or lower are the same as those in the first embodiment. The description is omitted.

FIG. 3 shows a flowchart of the fuel cell system according to Embodiment 2 of the present invention.

First, the controller 15 stops the power generation of the fuel cell 3 (step 202) when the predetermined time has elapsed (for example, reaches the first period) (step 201), and the oxidation of the fuel cell 3 is stopped. The oxidizing gas supplied to the cathode 2b by the agent gas supply unit 11 and the fuel gas supplied to the anode 2a by the fuel gas supply unit 10 are stopped (step 203), and the battery voltage detected by the voltage detector 14 is the second voltage. Wait until the voltage (about 0.2 V) or less (step 204).

When the battery voltage reaches the second voltage or lower, the anode inert gas supply unit 13 supplies an inert gas (desulfurized raw material gas) to the anode 2a, and the oxidant gas supply unit 11 supplies an oxidant gas to the cathode 2b. Supply (step 205), supply a constant amount necessary to replace the fuel gas remaining in the anode 2a with an inert gas, and cross-leak oxygen into the anode 2a to raise the electrode potential of the anode 2a. A certain amount of oxidant gas necessary to be supplied is supplied (step 206).

Since the operation sequence after step 207 is the same as that of the first embodiment, description thereof is omitted.

According to the fuel cell system of the second embodiment of the present invention having the above-described configuration, after stopping the power generation of the fuel cell 3, before increasing the electrode potential of the anode 2a and the cathode 2b, the oxidizing gas and the The supply of the fuel gas to the cathode 2b and the anode 2a is stopped, and oxygen remaining in the cathode 2b is reacted with hydrogen that cross-leaks from the anode 2a and consumed, so that the interface of the electrode of the cathode 2b The catalyst is reduced and the activity of the catalyst can be restored.

At this time, since the oxygen at the catalyst interface of the cathode 2b disappears, the electrode potential of the cathode 2b decreases, and the apparent battery voltage (potential difference between the anode 2a and the cathode 2b) detected by the voltage detector 14 decreases. After the battery voltage detected by the detector 14 reaches a second voltage (for example, 0.2 V) at which the activity of the catalyst of the cathode 2b is sufficiently recovered, the inert gas is supplied to the anode inert gas supply unit 13. Is supplied to the anode 2a, and the oxidant gas supply unit 11 again supplies a constant amount of oxidant gas to the cathode 2b to increase the electrode potentials of the anode 2a and cathode 2b, and the catalyst of the anode 2a and cathode 2b. Since the activity is kept high and impurities are oxidized and removed, a high battery voltage can be maintained for a long time, and a fuel cell system excellent in power generation efficiency and durability is obtained. Door can be. The second voltage may be lower than the power generation voltage during normal operation, and is preferably 0 V to 0.5 V, for example.

(Embodiment 3)
In the fuel cell system according to Embodiment 3 of the present invention, the controller 15 stops the power generation of the fuel cell 3 and stops the cooling of the fuel cell 3 cooled by the cooling unit 12 every time the first period elapses. Then, after the battery voltage of the fuel cell 3 detected by the voltage detector 14 falls below the second voltage and the temperature of the fuel cell 3 falls below the first temperature, the anode inert gas supply unit 13 The second embodiment is different from the second embodiment in that an inert gas is supplied to the anode 2a and an oxidizing gas is supplied to the cathode 2b by the oxidizing gas supply unit 11 in a certain amount.

The constituent elements other than the sequence until the temperature of the fuel cell 3 decreases to the first temperature or lower are the same as those in the second embodiment, and thus the description thereof is omitted.

FIG. 4 shows a flowchart of the fuel cell system according to Embodiment 3 of the present invention.

First, when the power generation time of the fuel cell 3 has elapsed (for example, reaches the first period) (step 301), the controller 15 stops the power generation of the fuel cell 3 and the fuel cell 3 The temperature of the fuel cell 3 is cooled using the cooling fluid (step 302). Then, the oxidant gas supplied to the cathode 2b by the oxidant gas supply unit 11 and the fuel gas supplied to the anode 2a by the fuel gas supply unit 10 are stopped (step 303), and the battery voltage detected by the voltage detector 14 is reduced. The process waits until the temperature is lower than the second voltage (about 0.2 V) and the temperature of the fuel cell 3 is lower than the first temperature (about 50 ° C.) (step 304).

Here, the first temperature is lower than the dew points of the fuel gas and the oxidant gas supplied to the anode 2a and the cathode 2b, and sufficient condensed water to wash away impurities adsorbed on the anode 2a and the cathode 2b. Is preferably at least 5 ° C. lower than the dew point temperatures of the anode 2a and the cathode 2b. The first temperature is preferably obtained experimentally in advance.

Since the operation sequence after step 305 is the same as that of the second embodiment, description thereof is omitted.

Next, in the fuel cell system configured as described above, a fuel cell system in which deterioration of the fuel cell 3 is estimated to have occurred due to actual accumulation of impurities, and the fuel cell 3 when the above operation sequence is applied. And the fluorine ion concentration in the drain water representing the deterioration of the fuel cell 3 were analyzed. For comparison, the same evaluation was performed on the behavior of the voltage change and fluorine ion concentration of the fuel cell system when the operation sequence was not included.

At this time, the utilization rate of the fuel gas supplied to the anode 2a side was 70%, the dew point was about 55 ° C., the utilization rate of the oxidant gas supplied to the cathode 2b side was 50%, and the dew point was about 65 ° C. Then, the load was controlled so that the current density was 0.2 A / cm 2 with respect to the electrode areas of the anode 2 a and the cathode 2 b so that the current flowed constant. The cooling fluid for cooling the fuel cell 3 has a cooling fluid flow rate of about 60 ° C. near the fuel cell cooling fluid channel inlet manifold and about 70 ° C. near the fuel cell cooling fluid channel outlet manifold. Controlled.

Then, the fluorine ion concentration contained in the drain water discharged from the anode 2a and the cathode 2b was measured while performing a power generation test.

FIG. 5 shows the measurement result of the fluorine ion concentration representing the voltage behavior from the stop to the start and the deterioration of the fuel cell 3 in which the impurity removal sequence is performed. As shown in FIG. 5, the power generation of the fuel cell 3 is stopped in step 302, and the battery voltage once rises to the open circuit voltage (about 1V) and then quickly decreases and falls below the second voltage (about 0.2V). It was. At this time, the oxygen remaining in the cathode 2b is consumed by reacting with hydrogen leaking from the anode 2a, and the catalyst of the cathode 2b is sufficiently reduced to increase its activity.

In step 305, the fuel gas remaining in the anode 2a in the anode inert gas supply unit 13 is replaced with the inert gas in step 305, and the oxidant gas is supplied again to the cathode 2b. Although the voltage close to the open circuit voltage is once generated due to the hydrogen remaining in the battery, the battery voltage decreases again because the hydrogen is immediately removed from the anode 2a. At this time, the anode 2a is oxidized by oxygen leaking from the cathode 2b, and the electrode potential of the anode 2a gradually rises and approaches the electrode potential of the cathode 2b to which air is supplied.

Then, when the electrode potential of the anode 2a rose to close to 1V, the battery voltage became about 0.1V or less which is the first voltage.

In step 309, when fuel gas and oxidant gas are respectively supplied to generate power again, an open circuit voltage is obtained, load is started, and power generation is resumed.

In addition, in the behavior of the fluorine ion concentration in the comparative example, no increase in the fluorine ion concentration was observed in the initial stage, but it was found that the fluorine ion concentration gradually increased after about 5,000 hours. . Then, when the behavior of the fluorine ion concentration was examined before and after this impurity removal sequence, the sequence for removing impurities was operated for the fuel cell system of Embodiment 3 of the present invention, as shown in FIG. The increase in the fluorine ion concentration of the fuel cell system according to Embodiment 3 of the present invention stopped, and the fluorine ion concentration decreased to almost the same level as the initial stage. On the other hand, it was found that the fluorine ion concentration continued to increase in the comparative example in which the normal start-stop was not performed without the sequence for removing impurities.

Therefore, according to the fuel cell system of the third embodiment of the present invention configured as described above, the water vapor and reaction contained in the fuel gas and the oxidant gas supplied during power generation when the power generation of the fuel cell 3 is stopped. The water vapor generated in step 1 is cooled and condensed, and condensed water is generated in each of the anode 2a and the cathode 2b. Water-soluble impurities, such as impurities remaining inside when the fuel cell 3 is produced, or impurities generated by thermal decomposition of members constituting the fuel cell 3 during operation of the fuel cell 3 are contained in this condensed water. Since it dissolves, the stopped condensed water that has absorbed this impurity can be discharged out of the system together with the inert gas or oxidant gas supplied in step 305.

(Embodiment 4)
In the fuel cell system according to Embodiment 4 of the present invention, the controller 15 supplies a certain amount of inert gas to the anode 2a by the anode inert gas supply unit 13, and then supplies the oxidant gas by the oxidant gas supply unit 11. The difference from Embodiment 3 is that a constant amount is supplied to the cathode 2b.

The constituent elements other than the order in which the inert gas and the oxidant gas are supplied are the same as those in the third embodiment, and thus the description thereof is omitted.

FIG. 6 shows a flowchart of the fuel cell system according to Embodiment 4 of the present invention.

Steps until power generation is stopped and the battery voltage of the fuel cell 3 becomes equal to or lower than the second voltage are the same as those in the third embodiment.

Then, when the battery voltage of the fuel cell 3 reaches the second voltage, the anode inert gas supply unit 13 supplies an inert gas to the anode 2a (step 405), and a certain amount of inert gas replacing the remaining fuel gas. After supplying the active gas (step 406), the inert gas supplied by the anode inert gas supply unit is stopped, and the oxidant gas is supplied to the cathode 2b by the oxidant gas supply unit 11 (step 407).

When a certain amount of oxidant gas is supplied (step 408), the supply of oxidant gas is stopped (step 409), oxygen is cross-leaked from the cathode 2b, and the electrode potential of the anode 2a is raised.

Since step 410 and subsequent steps are the same as those in the third embodiment, description thereof is omitted.

According to the fuel cell system of Embodiment 4 of the present invention configured as described above, the anode inert gas supply unit 13 replaces the fuel gas containing hydrogen remaining on the anode 2a with the inert gas, and reacts with oxygen. Then, the supply of the inert gas is stopped, the internal pressure of the anode 2a is lowered, and then the oxidant gas supply unit 11 supplies air to the cathode 2b. The amount of oxygen leaking can be increased, the electrode potential of the anode 2a can be increased in a shorter time, and the time during which the catalyst of the anode 2a is exposed to a high potential can be shortened. Can be further suppressed.

(Embodiment 5)
In the fuel cell system according to Embodiment 5 of the present invention, the controller 15 has the cooling unit so that the temperature of the fuel cell 3 becomes equal to or lower than the first temperature before the second period when the first period elapses. 12 is different from Embodiment 3 in that the power generation of the fuel cell is stopped after generating power for the second period.

The constituent elements other than the point of lowering the temperature of the fuel cell 3 before stopping the power generation of the sequence for removing the impurities are the same as those in the third embodiment, and thus the description thereof is omitted.

FIG. 7 shows a flowchart of the fuel cell system according to Embodiment 5 of the present invention.

First, the controller 15 performs a predetermined time before a predetermined time (for example, before the second period (several tens of minutes to the first period in which an amount of impurities that does not affect the deterioration of the fuel cell 3 is accumulated). (Several tens of hours ago))) (step 501), the cooling fluid pump 122 of the cooling unit 12 is controlled so that the temperature of the fuel cell 3 decreases, and the temperature of the fuel cell 3 is set to the first temperature. Cool to a temperature (about 50 ° C.) or lower (step 502).

Here, the first temperature is lower than the dew points of the fuel gas and the oxidant gas supplied to the anode 2a and the cathode 2b, and there is sufficient condensed water to wash away impurities adsorbed on the anode 2a and the cathode 2b. It is a temperature to be generated and is preferably at least 5 ° C. lower than the dew point temperature of the anode 2a and the cathode 2b, and is preferably a temperature at which flooding does not occur. The first temperature is preferably obtained experimentally in advance.

Then, after a predetermined time (for example, the second period) elapses while the temperature of the fuel cell 3 is low (step 503), the power generation is stopped (step 504). Since the subsequent steps after power generation is stopped are the same as those in Embodiment 3, the description thereof is omitted.

According to the fuel cell system of the fifth embodiment of the present invention configured as described above, the temperature of the fuel cell 3 is controlled to be equal to or lower than a predetermined temperature before power generation is stopped, and the anode 2a and the cathode 2b are in an excessively humid state. Thus, a large amount of condensed water is generated at the anode 2a and the cathode 2b. By continuing the power generation in the second period in this state, the contamination of the anode 2a and the cathode 2b is absorbed by the condensed water, and the fuel gas and the oxidant are respectively The amount of contamination can be further reduced by the time gas is discharged out of the system together with the gas and power generation stops.

(Embodiment 6)
In the fuel cell system according to Embodiment 6 of the present invention, the controller 15 controls the cooling unit 12 so that the temperature of the fuel cell 3 is equal to or lower than the second temperature when the power generation of the fuel cell 3 is resumed. The third embodiment is different from the third embodiment in that power is generated in the third period.

Note that the components other than the point of generating power by lowering the temperature of the fuel cell 3 at the time of startup are the same as those in the third embodiment, and thus the description thereof is omitted.

FIG. 8 shows a flowchart of the fuel cell system according to Embodiment 6 of the present invention.

After the power generation is stopped, the steps up to the step of supplying the inert gas and the oxidant gas to the anode 2a and the cathode 2b, respectively, to make the voltage lower than the first voltage are the same as in the third embodiment, and the description is omitted.

When the battery voltage detected by the voltage detector 14 becomes equal to or lower than the first voltage (step 608), the controller 15 causes the temperature of the fuel cell 3 to become equal to or lower than the second temperature (room temperature to about 50 ° C.). Control such as quickly turning the cooling fluid pump 122 of the cooling unit 12 is performed (step 609).

Here, the second temperature is lower than the dew points of the fuel gas and the oxidant gas supplied to the anode 2a and the cathode 2b, and there is sufficient condensed water to wash away impurities adsorbed on the anode 2a and the cathode 2b. It is a temperature to be generated and is preferably at least 5 ° C. lower than the dew point temperature of the anode 2a and the cathode 2b, and is preferably a temperature at which flooding does not occur. The second temperature is preferably obtained experimentally in advance.

Then, fuel gas and oxidant gas are supplied in a state where the temperature of the fuel cell 3 is low (step 610), and power generation is resumed (step 611).

Then, power generation is performed in a state where the temperature of the fuel cell 3 is low, and when a predetermined time (for example, the third period (several minutes to several hours)) has elapsed (step 612), the temperature of the fuel cell 3 is changed to normal The temperature is returned to the same temperature (step 613).

According to the fuel cell system of the sixth embodiment of the present invention having the above-described configuration, power is generated with the temperature of the fuel cell 3 being low at the time of start-up, the anode 2a and the cathode 2b are in an excessively humid state, and the anode 2a and the cathode 2b A large amount of condensed water is generated, and the contamination of the anode 2a and the cathode 2b is absorbed by the condensed water and discharged together with the fuel gas and the oxidant gas, respectively, and the amount of contamination can be reduced.

(Embodiment 7)
In the fuel cell system according to Embodiment 7 of the present invention, the components other than the anode inert gas supply unit 13 supplying the inert gas to the anode 2a via the fuel gas supply unit 10 are the same as those in Embodiment 1. Since it is the same as that of FIG.

FIG. 9 shows a schematic configuration diagram of a fuel cell system according to Embodiment 7 of the present invention.

With this configuration, it is not necessary to add a configuration for supplying the inert gas directly to the anode 2a of the fuel cell 3, so that the fuel cell system can be simplified, the cost can be reduced, and the fuel gas supply unit 10 is also inert. Since it is purged with gas, deterioration due to oxidation of the catalyst used in the fuel gas supply unit 10 can be suppressed, and the durability of the fuel cell system can be further improved.

In the first to seventh embodiments of the present invention, the source gas is used as the inert gas, but the present invention is not limited to this. The inert gas is a gas other than the reducing gas supplied to the anode, and may be any gas that has chemical stability and does not chemically react with the anode itself in the environment where the fuel cell system is stopped. As the inert gas, for example, nitrogen gas, rare gas, or the like can be used in addition to the source gas.

In the first to seventh embodiments of the present invention, the desulfurizer 101, the raw material gas supply unit 102 and the hydrogen generator 103 are used as the fuel gas supply unit 10, and the desulfurizer 101 and the anode inert gas supply unit 13 are used. Although the raw material gas supply unit 102 is used, the present invention is not limited to this. For example, the fuel gas supply unit 10 may be a hydrogen cylinder that supplies hydrogen, and the anode inert gas supply unit 13 may be an inert gas cylinder that supplies an inert gas.

Also, it is preferable to use a raw material gas as the inert gas from the viewpoint of simplifying the configuration of the fuel cell system and reducing the cost. As the source gas, a gas containing a hydrocarbon such as methane, propane, or butane can be used. For example, city gas, natural gas, liquefied propane gas, or the like can be used. Further, when the raw material gas contains a sulfur component, it is preferable to use a raw material gas in which the concentration of the sulfur component is reduced using a desulfurizer.

As described above, the fuel cell system according to the present invention is hardly affected by deterioration due to impurities, and a fuel cell, a fuel cell device, and a stationary fuel using a polymer type solid electrolyte that are required to be improved in durability. It can also be used for applications such as battery cogeneration systems.

2a Anode 2b Cathode 3 Fuel cell 10 Fuel gas supply unit 11 Oxidant gas supply unit 12 Cooling unit 13 Anode inert gas supply unit 14 Voltage detector 15 Controller

Claims

A fuel cell having an anode and a cathode;
A fuel gas supply unit for supplying a fuel gas containing at least hydrogen to the anode;
An oxidant gas supply unit for supplying an oxidant gas containing at least oxygen to the cathode;
An anode inert gas supply unit for supplying an inert gas to the anode and replacing at least a part of the fuel gas with the inert gas;
A voltage detector for detecting a battery voltage of the fuel cell;
A controller for controlling operations of the fuel cell, the fuel gas supply unit, the oxidant gas supply unit, and the anode inert gas supply unit;
With
The controller is
Performing a stop operation to stop power generation of the fuel cell;
Thereafter, the fuel gas supply unit stops supplying the fuel gas to the anode, the anode inert gas supply unit supplies the inert gas to the anode, and the oxidant gas supply unit Supplying the oxidant gas to the cathode, performing an activity recovery operation,
After the battery voltage of the fuel cell detected by the voltage detector drops below a first voltage, the fuel gas supply unit restarts the supply of the fuel gas supplied to the anode, and the fuel cell Control to resume power generation,
Fuel cell system.
The controller is
The power generation of the fuel cell is stopped, the supply of the oxidant gas supplied to the cathode by the oxidant gas supply unit is stopped, and the supply of the fuel gas supplied to the anode by the fuel gas supply unit is stopped. , Stop operation,
2. The fuel cell system according to claim 1, wherein the activation recovery operation is controlled after the battery voltage of the fuel cell detected by the voltage detector has decreased to a second voltage or less.
A cooling unit for cooling the fuel cell;
A temperature detector for detecting the temperature of the fuel cell;
With
The controller is
Stop the power generation of the fuel cell, and perform the stop operation to control the cooling unit to cool the fuel cell,
3. The fuel cell system according to claim 1, wherein after the temperature of the fuel cell detected by the temperature detector drops below a first temperature, control is performed to perform the activity recovery operation. 4.
A cooling unit for cooling the fuel cell;
A temperature detector for detecting the temperature of the fuel cell;
With
The controller controls the cooling unit so that the temperature of the fuel cell detected by the temperature detector is equal to or lower than the first temperature, and performs power generation of the fuel cell for a second period. , Stop power generation of the fuel cell, perform the stop operation,
4. The fuel cell system according to claim 3, wherein control is performed to perform the activity recovery operation thereafter.
A cooling unit for cooling the fuel cell;
A temperature detector for detecting the temperature of the fuel cell;
With
The controller, during the startup operation of the fuel cell,
The control unit according to any one of claims 1 to 4, wherein the cooling unit is controlled so that the temperature of the fuel cell is equal to or lower than a second temperature, and the power generation of the fuel cell is controlled to be performed for a third period. Fuel cell system.
The controller stops the supply of the fuel gas supplied to the anode by the fuel gas supply unit, and the oxidant gas supply after the anode inert gas supply unit supplies the inert gas to the anode. The fuel cell system according to any one of claims 1 to 5, wherein the control unit performs a recovery operation of supplying an oxidant gas to the cathode.
The controller according to any one of claims 1 to 6, wherein the controller performs the stop operation every time the first period elapses, and thereafter controls to restart the power generation of the fuel cell after performing the activity recovery operation. The fuel cell system according to any one of the above.
8. The fuel cell system according to claim 7, wherein the first period controlled by the controller is a time when a power generation time integrated value obtained by integrating the power generation time of the fuel cell reaches a predetermined power generation integrated time.
The anode inert gas supply unit includes a desulfurizer for desulfurizing the raw material gas,
The fuel cell system according to any one of claims 1 to 8, wherein the inert gas is a raw material gas desulfurized by the desulfurizer.
The fuel cell system according to any one of claims 1 to 9, wherein the anode inert gas supply unit is configured to supply the inert gas to the anode via the fuel gas supply unit.
An operating method of a fuel cell system comprising a fuel cell having an anode and a cathode, supplying a fuel gas containing at least hydrogen to the anode, and supplying an oxidant gas containing at least oxygen to the cathode to generate electric power,
A stop step of stopping power generation of the fuel cell;
Thereafter, stopping the supply of the fuel gas to the anode, supplying the inert gas to the anode, and supplying an oxidant gas containing at least oxygen to the cathode;
A restarting step of restarting the supply of the fuel gas supplied to the anode and restarting the power generation of the fuel cell after the battery voltage of the fuel cell drops below a first voltage;
With
Operation method of fuel cell system.
The stopping step is a step of stopping power generation of the fuel cell, stopping supply of the oxidant gas supplied to the cathode, and stopping supply of the fuel gas supplied to the anode,
12. The method of operating a fuel cell system according to claim 11, wherein after the stop step, the activation recovery step is performed after the battery voltage of the fuel cell has dropped below a second voltage.
The stopping step is a step of stopping power generation of the fuel cell and cooling the fuel cell;
The operation method of the fuel cell system according to claim 11 or 12, wherein the activity recovery step is performed after the temperature of the fuel cell is lowered to a first temperature or lower.
Cooling the fuel cell such that the temperature of the fuel cell is equal to or lower than the first temperature;
Performing the stopping step of stopping the power generation of the fuel cell after performing the power generation of the fuel cell for the second period;
The operation method of the fuel cell system according to claim 13, wherein the activity recovery step is performed thereafter.
During the start-up operation of the fuel cell,
The fuel cell according to any one of claims 11 to 14, wherein the fuel cell is cooled so that the temperature of the fuel cell is equal to or lower than a second temperature, and the power generation of the fuel cell is performed for a third period. How to operate the system.
In the activity recovery step, the fuel gas supply unit stops supplying the fuel gas supplied to the anode, and the anode inert gas supply unit supplies the inert gas to the anode, and then the oxidant gas. The method of operating a fuel cell system according to any one of claims 11 to 15, wherein the supply unit is a step of supplying the oxidant gas to the cathode.
The fuel cell system according to any one of claims 11 to 16, wherein the stop step is performed each time the first period elapses, and then the resumption step is performed after performing the activity recovery step.
The fuel cell system operating method according to claim 17, wherein the first period is a time when a power generation time integrated value obtained by integrating the power generation time of the fuel cell reaches a predetermined power generation integrated time.